1. Field of the Invention
This invention relates generally to an improved one-component lubricative and protective coating for a magnetic recording medium, and more particularly to a fingerprint and moisture resistant lubricant and coating for a floppy disk.
2. Description of the Prior Art
There is a rapidly growing demand for more effective types of storage media for microcomputers. Various devices and methods have been created to handle the storage of large quantities of information. Typically, information is stored on disk storage media, either a hard Winchester disk or a soft floppy disk. Floppy disks are slower than the hard disks and generally less reliable. Floppies also have more limited storage; currently in the range of 160-640 kilobytes. Floppies are also much less expensive than hard disks, but due to their construction and mode of use are very prone to wear and contamination from the environment, for example from fingerprints and coffee spills. Floppy disks also tend to deform under humidity and temperature changes causing the disk to swell or shrink which shifts the narrow tracks. Such environmental contamination and hygroscopic effects can result in serious consequences on the readability of the disk. As disk manufacturers look to higher bit densities to increase storage space, it becomes more critical to protect the disk from contamination and to ensure correct head tracking. Additionally, the disks are interfaced by a read/write head which contacts the disk when the disk starts and stops its high speed rotation. Thus the disk may have a lubricant layer to reduce the frictional engagement therewith. Any lubricant coating on a magnetic recording medium must, however, be firmly bonded to the medium to prevent its accumulation on the head. The magnetic recording medium itself, consisting of minute particles of an oxide of iron or other metal, is highly abrasive to the head, and will rapidly degrade the head if it is not protected. Typically liquid lubricants are employed, but these require binders to maintain them in adherence to the medium. Despite the binders, the relatively high vapor pressures of many lubricants precludes their effectiveness over protracted periods. Solid lubricants have had only limited success, primarily because their inherent lack of flowability requires thick layers, increasing the gap spacing and thus decreasing magnetic impulse transfer between the head and the medium.
Floppy disks are typically constructed of a polyethylene terephthalate (PET) film known by the trade name Mylar, or a similar material, coated with a magnetic medium on which information may be stored and from which information may be retrieved. The magnetic medium, is a ferromagnetic recording medium and typically is a ferric oxide coating. This medium itself is sensitive to abrasion and environmental damage and to ensure its longevity it must be protected. This is accomplished in part by enclosing the disk in a jacket. The disk however is also susceptible to damage in use from pressure exerted by the read/write heads and by human handling. Accordingly it is advantageous to provide the disk itself with a protective coating. Typically the lubricant applied to the surface of the disk may have some protective qualities but such lubricants are primarily intended to reduce the frictional engagement of the read/write head with the surface of the disk, and are not protective in function.
Typical prior art approaches to coatings for magnetic recording media involve a liquid lubricant, applied to the surface of the medium. U.S. Pat. No. 3,490,946 issued to Wolff, discloses a fluorocarbon polymer dispersed in a relatively non-volatile fluorocarbon carrier. Wolff is intended and acts as a lubricant coating, and does not disclose any protective effects. Wolff also requires a binder in application of the lubricant, as the lubricant is a liquid. U.S. Pat. No. 4,188,434 issued to Loran utilizes a liquid lubricant, although a solid lubricant is also included. Other references, for example U.S. Pat. No. 3,998,989 issued to Pardee disclose similar combinations of lubricating agents i.e. solid-liquid or liquid-liquid mixtures. The Pardee patent, as well as a second Pardee U.S. Pat. No. 4,232,072 are designed primarily for substrates other than magnetic recording media, such as photographic film and thermoplastic materials including phonograph records.
U.S. Pat. Nos. 4,390,562 issued to Yanagisawa and 4,330,150 issued to Dorrell relate to lubrication of metal surfaces and not to magnetic recording media. Other approaches include that of Schoettle et al (U.S. Pat. No. 4,254,585) which describes a burnishing, cleaning and calendaring process without the use of a coating for treating magnetic media, and Yamada (U.S. Pat. No. 4,391,851) which is a means of producing a high density magnetic coating on a tape.
In view of the prior art, the problem of providing an effective protective coating for flexible magnetic storage media still exists. None of the prior art disclose a coating which is resistant to environmental contaminants and which does not interfere with disk readability.